This invention relates to the detection of proteins by the utilization of the phenomenon by which such proteins interact specifically either immunologically or non-immunologically.
The use of small magnetic particles coated with a protein that will interact specifically with a select protein in order to separate such select protein from a solution is disclosed in U.S. Pat. No. 4,018,886 -- Giaever. Also, the use of small magnetic particles coated with an antibody layer for sorting out and separating select viruses, bacteria and other cells from multi-cell, bacteria or virus populations is disclosed in U.S. Pat. No. 3,970,518 -- Giaever.
In U.S. Pat. No. 3,933,997 -- Hersh et al., composites consisting of antidigoxin antibodies coupled chemically through an intermediate silane coupling agent to magnetically responsive inorganic particles are employed for the determination of the concentration of digoxin utilizing a standard digoxin assay curve. The above-noted patents are incorporated by reference.
A common test for pregnancy involves coating small polystyrene latex spheres with the enzyme, human chorionic gonadotropin (HCG). When a woman becomes pregnant the level of HCG in the urine increases significantly. This is an indirect test in which a quantity (as determined by titer by an established procedure) of antibodies to HCG is added to a sample of female urine and is allowed to incubate for from about 5 to about 10 minutes therein. Next, HCG-covered latex spheres are mixed with the urine and the mix is allowed to incubate for from about 5 to about 10 minutes. If agglutination of the spheres takes place, the urine does not contain HCG to the level establishing a pregnant condition; if the spheres remain in single suspension, HCG was present beyond that level. Potentially this is a very sensitive and simple immunological test, but it often runs into trouble because the determination as to whether the spheres have agglutinated or not requires a subjective judgment on the part of the technician.
It would be of particular advantage to provide a more objective test of this general type and, preferably, a test, which reduces the incidence of non-specific reactions by which sticking of proteins to the spheres, or particles, occurs.